This paper proposes a dynamic system, with an associated fusion learning inference procedure, to perform real-time detection and localization of nuclear sources using a network of mobile sensors. This is motivated by the need for a reliable detection system in order to prevent nuclear attacks in major cities such as New York City. The approach advocated here installs a large number of relatively inexpensive (and perhaps relatively less accurate) nuclear source detection sensors and GPS devices in taxis and police vehicles moving in the city. Sensor readings and GPS information are sent to a control center at a high frequency, where the information is immediately processed and fused with the earlier signals. We develop a real-time detection and localization method aimed at detecting the presence of a nuclear source and estimating its location and power. We adopt a Bayesian framework to perform the fusion learning and use a sequential Monte Carlo algorithm to estimate the parameters of the model and to perform real-time localization. A simulation study is provided to assess the performance of the method for both stationary and moving sources. The results provide guidance and recommendations for an actual implementation of such a surveillance system.Appl. Stochastic Models Bus. Ind. 2018, 34 4-19 GRELAUD ET AL. t ), of all the sensors in the system and the binary signals the sensors send to the control center t = (d (1) t , · · · , d (n t ) t ). Here, n t is the number of active sensors. The locations, t , are assumed to be accurate, but the signals received by the control center could possibly be false.This model assumes the presence of one source. It is compared with the baseline model, where no source is present, for the purpose of detecting the presence of a source. Details of the comparison are presented in Section 3.2. The extension to multiple source detection is discussed in Section 6.State-space models have been widely used in many applications, including source tracking [29,30,[36][37][38][39][40][41][42][43]. However, our approach is different from standard source tracking problems, mainly because in our case, both negative and positive binary signals are observed and used. The use of state-space formation allows the data collected at time t to be used for the estimation of the location of the source x t with the information observed in the past, through an updating of the previous estimation of x t−1 , instead of performing an independent analysis at each time point. A source's motion possesses 6